9 Chapter 9: Estimating body composition

Melissa Markofski


Body composition and anthropometric measures

There are many ways to assess body composition and anthropometric measures. Some of these methods require expensive, highly specialized equipment, while other methods are simple and use inexpensive equipment. When evaluating a person’s progress and taking measurements before, during, and after a training program, the method does not matter as much as using the same method for all timepoints and being accurate (reliable) in your measurements. 

Anthropometric measures are: height, weight, BMI, body circumferences, and skinfold thickness. It is important to make the distinction that skinfold thicknesses are anthropometric measures, but when the skinfold thickness measures are used to calculate an estimation of body fat then body fat measurement is not an anthropometric measure.

Anthropometric measurements are simple, easy measurements that can help additionally classify a person’s health. The waist to hip ratio is calculated from measurements of the circumference of the waist (narrowest point of midsection) and hips (widest circumference around pelvis). A ratio of greater than 0.95 for males and 0.86 for females is considered an increased risk for CVD.

Circumference anthropometric measurements can also be used to track fitness. It can be used as a crude estimate of fat loss and/or muscle gains. These measurements are typically taken around the belly of the muscle group of interest, such as the thigh or upper arms.

Regardless of the method for assessing body composition, each method is estimating body composition. We are not physically dividing the body into lean mass and non-lean mass and weighing it. Care also needs to be taken to decide if the estimated body composition measures should be expressed as absolute or relative values.


Class activity

Estimated body composition

Activity 1: Air displacement plethysmography (BodPod GAR 124)

ADP measures body volume and body density to estimate body composition. You will watch a demonstration of the BodPod on one person.


Activity 2: Bioelectrical impedance (BIA)

BIA uses resistance of an electrical current to estimate body composition. Muscle contains more water than adipose tissue, and therefore muscle will resist the electrical current less than adipose tissue. However, hydration status is an important factor in obtaining an accurate measurement.

To use the BIA, you will need to be barefoot. The machine will walk you through the input.

1) Turn on unit with on/off button

2) Enter clothes weight (typically 2 lbs)

3) Enter sex and body type by pressing the corresponding key. Use “athletic” if you are involved in at least 10 hours of intense physical activity a week, or have a lifetime of fitness (have had this level of activity for 5+ years, but are not presently reaching this amount of activity).

4) Enter age, in years

5) Enter height in feet then inches

6) Step on scale and be still until the unit prints your results.

7) Clean the scale (spray paper towel with cleaner—not the BIA!—and wipe the contacts).



Activity 3: Skinfold calipers

Skinfold calipers can also be used to calculate relative body fat. In class today we will use the three site method, with specific locations for males or females. You may wish to review the “How to Measure Skinfolds” box on page 194 of your text prior to starting the measurements.


  1. Collect measurements of basic body dimensions (height and weight)
  2.  Use the skinfold calipers to measure skinfold thickness (mm) For men measure chest, abdomen, and thigh. For women measure triceps, suprailiac crest, and thigh.
  3. Collect each measurement three times from each sit (rotate sites i.e. collect all of the three sites once, then again, then a third time).
  4. Use your textbook table 7.7 to refresh your memory of where the specific sites are located, paying attention to the orientation of the measurement (horizontal, diagonal, etc.).
  5. Calculate body density (sum3 = sum of the three skinfold sites)


Calculation of body density (Db) to 5 significant figures:

Skinfold Thickness (Jackson & Pollock):   Db= _______________gm/cc

males = 1.109380 – (0.0008267 x sum3) + (0.0000016 x sum32) – (0.0002574 x age)

Females = 1.0994921 – (0.0009929 x sum3) + (0.0000023 x sum32) – (0.0001392 x age)


6. Calculation of relative body fat (Siri) males: (495 / Db) – 450 = ________%

Calculation of relative body fat (Siri) females:  (509 / Db) – 450 = ________%

7.Calculation of fat weight (FW): body weight  x  % fat

8. Calculation of fat free weight (FFW): body weight – fat weight

9. Calculation of optimal or desirable body weight:

Target body weight = current fat free wt. /  %FFM goal


Anthropometric measurements

Activity 4:  circumference measurements

Use your textbook Table 7.3 to refresh your memory of how to conduct this measurement.

  1. Take each measurement on one of your classmates twice. Collect measures of waist, hip, thigh, and upper arm.
  2. If the sites differ by more than 2 cm, take a third and average the two within 2 cm.
  3. Use the averages of the hip and waist to calculate the waist:hip ratio



Activity 5: Coefficient of variation

There can be much variation in methods. The coefficient of variation is expressed as a percent and can help us determine the repeatability of the measurement (and precision). At the end of lab, calculate the coefficient of variation using your body compositions measurements (of the same person, hopefully you) from BIA and skinfold measurements.

coefficient of variation of sample = standard deviation of sample / mean of sample

Note: standard deviation of sample = square root of [(the variance)/(n-1)]

where n = number of samples

variance =  add the squares of each difference between each sample and the mean



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